1. Field of the Invention
This invention relates to dial register apparatus and more particularly to an improved pawl member and a ratchet assembly to convert a bidirectional rotational input to unidirectional rotation of the register apparatus.
2. Description of the Prior Art
Unidirectional register apparatus are designed to totalize and display the measured value of variable quantities such as the consumption of water, gas or electricity. Watthour meters include such apparatus for measuring and totalizing AC electric energy consumption. The present invention is of particular advantage in a watthour meter and preferred embodiments thereof are described for use in such a meter.
In a conventional watthour meter, voltage and current magnetic sections produce alternating magnetic fluxes responsive to the line voltage and line current. The fluxes rotate an electroconductive disc which is in driving relationship with a register. If the direction of rotation of the electroconductive disc is reversed from the direction that produces a true registration, then the registration provided prior to such reversal is reduced by the amount of such reversed rotation. In order to prevent such false registrations, it is well known to use a ratchet device for providing a unidirectional rotation of a prior art register in response to bidirectional rotation of the electroconductive disc. Such a ratchet device is disclosed in U.S. Pat. No. 2,922,111, assigned to the assignee of this invention. Unidirectional rotation of the register is maintained by a pair of separate and opposing pawl and ratchet wheel assemblies. The patent teaches that the width of each pawl is thick relative to its length.
It is also known to maintain unidirectional rotation by using a single pivotal pawl having two symmetrical ends wherein each pawl end engages one of two opposing sets of ratchet teeth. The engagement of a particular set of ratchet teeth depends upon the direction of rotation of the input. Such a device is disclosed in U.S. Pat. No. 825,791 wherein the width of the pawl is thick relative to its length. Furthermore, the pawl is not part of the driving member but is driven by the ratchet teeth adjacent the pawl.
In U.S. Pat. No. 2,687,658, an alternate embodiment uses a thin pivotal pawl to maintain unidirectional rotation from a bidirectional input by alternately engaging recesses in opposing drive members. The pawl is made of a torsional spring for maintaining its ends in an expanded position and for ensuring that its free end will engage a recess in the opposing drive member when the direction of rotation of the input is reversed.
When coupled with a register apparatus, none of the aforementioned prior art ratchet devices maintain unidirectional rotation as efficiently and reliably as the present invention.